1. Field of the Invention
The present invention pertains to amusement devices employing a signal transmitter and receiver operating in the optical spectrum, and more particularly to an amusement park shooting gallery system using light guns.
2. Description of the Prior Art
Many prior art optical transmission systems in amusement devices are responsive to continuous light and the receivers in such systems are subject to being triggered by spurious or random light. Even in systems where frequency gating is employed, conventional gating systems allow false triggering. A principal reason for the registration of false hits in conventional systems is that the 60 cycle 120 volt a.c. current, typically used as a primary power source, generates harmonic frequencies in the gating system. Conventional optical transmission systems in amusement devices typically employ mechanical shutters. For example, U.S. Pat. No. 4,054,290 describes such a gating system in which the sensitive frequency is 400 hertz. This system uses a tuning fork to physically and intermittently block an aperture through which light is transmitted.
Because of the low triggering frequency employed in conventional amusement devices that utilize frequency gating, the harmonics developed from the 60 cycle a.c. power supply are of a sufficient strength to trigger the receiver and cause the registration of false hits. It should be noted that the strength of a harmonic signal will decrease with increased frequency above the base signal. That is, the first harmonic of a 60 hertz signal is 120 hertz, and is stronger than the second harmonic, which is 240 hertz. Similarly, the second harmonic is stronger than the third harmonic of 480 hertz. It should also be noted, especially when dealing with an unregulated 60 hertz supply, that complex frequencies are likely occur to approximate almost any frequency. Thus, even when no exact integral harmonic of the a.c. supply corresponds precisely to a triggering frequency, such as the 400 hertz system described in U.S. Pat. No. 4,054,290, the combined frequencies of the harmonics produced do approximate almost any frequency. Conventional frequency sensitive receivers in amusement devices have heretofore been set at frequencies far too low to avoid the effects of combined harmonics of the operating power source and other spurious noise.
For particular applications, such as the use of a light gun for amusement park shooting galleries, such prior art systems have further disadvantages in that a continuously generated light beam, pulsed or not, permits the shooter to hunt around the target with the beam on until the target is hit.
Thus, for particular applications, such as light guns for shooting galleries, there has long been a need for a system which permits the transmitting gun to emit optical energy for only a brief period of time when the trigger is pulled and a receiving target which is not responsive to spurious light or noise harmonics. The present invention satisfies that need.